With this tool you can very easy find what demand you should have of the components of a Newton telescope.

I have never done this before so it's a trail and error process.
And I don't think I ever will built a telescope from scratch, just more to collect information and knowledge what to look after
when buying a telescope.

Note:
Don't build a telescope after my ideas before you know by yourself that it will work.
Otherwise you will waste a lot of time and money!